Phonons: Theory and Experiments I

Brüesch, P.

doi:10.1007/978-3-642-81781-6

Cited by 251 publications

(149 citation statements)

References 16 publications

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“…12,13,16,[18][19][20][21][22] These interactions along [100] crystallographic directions cause the transverse optic (TO) phonon branch to dip to low energy at the zonecenter. The strong anharmonicity causes this zone-center TO phonon to stiffen markedly as T increases in the cubic paraelectric phase, in a clear departure from a quasiharmonic lattice, 10,[23][24][25][26][27] but in general agreement with the soft-mode picture of the ferroelectric transition. 28,29 Recently, an asymmetry of peaks was reported in the pair-distribution-function (PDF) or radial distribution function (RDF) of PbTe, PbS, and SnTe, which was interpreted in terms of atomic off-centerings increasing with temperature.…”

Section: Introductionmentioning

confidence: 65%

Anharmonicity and atomic distribution of SnTe and PbTe thermoelectrics

Cao

et al. 2014

Phys. Rev. B

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The structure and lattice dynamics of rock-salt thermoelectric materials SnTe and PbTe are investigated with single crystal and powder neutron diffraction, inelastic neutron scattering (INS), and first-principles simulations. Our first-principles calculations of the radial distribution function (RDF) in both SnTe and PbTe show a clear asymmetry in the first nearest-neighbor (1NN) peak, which increases with temperature, in agreement with recent experimental reports. We show that this peak asymmetry for the 1NN Sn-Te or Pb-Te bond results from large-amplitude anharmonic vibrations (phonons). No atomic off-centering is found in our simulations. In addition, the atomic mean square displacements derived from our diffraction data reveal stiffer bonding at the anion site, in good agreement with the partial phonon densities of states from INS, and first-principles calculations. These results provide clear evidence for large-amplitude anharmonic phonons associated with the resonant bonding leading to the ferroelectric instability.

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Section: Introductionmentioning

confidence: 65%

Anharmonicity and atomic distribution of SnTe and PbTe thermoelectrics

Cao

et al. 2014

Phys. Rev. B

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“…Typically, it takes a positive value, γ ∼ 1.5, and depends weakly on temperature. It provides a measure of anharmonicity, because phonon frequencies do not depend on volume in a perfectly harmonic lattice (21,23). The widely used quasiharmonic (QH) approximation assumes that the temperature dependence of phonon frequencies arises solely from changes in volume.…”

Section: Anomalous Phonon Softeningmentioning

confidence: 99%

Phonon softening and metallization of a narrow-gap semiconductor by thermal disorder

Delaire

Marty

Stone

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

110

109

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The vibrations of ions in solids at finite temperature depend on interatomic force-constants that result from electrostatic interactions between ions, and the response of the electron density to atomic displacements. At high temperatures, vibration amplitudes are substantial, and electronic states are affected, thus modifying the screening properties of the electron density. By combining inelastic neutron scattering measurements of Fe 1−x Co x Si as a function of temperature, and finite-temperature first-principles calculations including thermal disorder effects, we show that the coupling between phonons and electronic structure results in an anomalous temperature dependence of phonons. The strong concomitant renormalization of the electronic structure induces the semiconductor-to-metal transition that occurs with increasing temperature in FeSi. Our results show that for systems with rapidly changing electronic densities of states at the Fermi level, there are likely to be significant phonon-electron interactions, resulting in anomalous temperature-dependent properties.electron-phonon coupling | metal-insulator transition | thermoelectrics B ecause many properties of the solid state derive from the electronic structure (1), understanding finite temperature effects on the band structure is crucial to accurately describe materials in realistic operating conditions. The effects of thermal disorder on the electronic structure of materials at high temperature are largely unexplored, however, and the role of the electron-phonon interaction above room temperature has remained controversial (2-5). We performed detailed investigations of the phonons and electronic structure in Fe 1−x Co x Si and found that an adiabatic coupling can lead to pronounced anomalies in the temperature dependence of both phonons and electron states. The mechanism is general and could affect a broad class of materials, including narrow-gap semiconductors, superconductors, heavy-Fermion compounds, and thermoelectrics.FeSi has attracted a great deal of interest as it exhibits an insulator-metal transition with increasing temperature, and many of its physical properties show anomalous temperature dependences, including the magnetic susceptibility, heat capacity, Seebeck coefficient, thermal expansion, and elastic properties (6-11). Recently, it has been argued that doping FeSi with Al can lead to a surprising heavy-Fermion metal (12). FeSi has also attracted attention as a possible reaction product at Earth's core-mantle boundary (13-16), and as a candidate thermoelectric material for refrigeration applications (9). The compounds FeSi and CoSi are isostructural, crystallizing in the cubic B20 structure, with similar ion coordinates (17, 18). Although FeSi undergoes a gradual transition from narrow-gap semiconductor (E gap ∼ 0.1 eV) to metal with increasing temperature, the additional d electron in CoSi leads to a metallic state at all temperatures. The anomalous temperature dependences observed in FeSi are absent in CoSi.Here, we show that the adia...

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“…The model parameters are given in Table II, the crystal structure data were taken from reference [31]. We use a shell model [33] with Born-Mayer potentials describing the repulsive interactions. The shell charges of Nd and Cu and the amplitude of the O-O Born-Mayer potential were slightly adapted.…”

Section: Iii1 Phenomenological Modelmentioning

confidence: 99%

Dispersion of the high-energy phonon modes inNd1.85Ce0.15CuO4

et al. 2005

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The dispersion of the high-energy phonon modes in the electron doped high-temperature superconductor Nd1.85Ce0.15CuO4 has been studied by inelastic neutron scattering. The frequencies of phonon modes with Cu-O bond-stretching character drop abruptly when going from the Brillouin zone center along the [100]-direction; this dispersion is qualitatively similar to observations in the hole-doped cuprates. We also find a softening of the bond-stretching modes along the [110]-direction but which is weaker and exhibits a sinusoidal dispersion. The phonon anomalies are discussed in comparison to hole-doped cuprate superconductors and other metallic perovskites.

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Phonons: Theory and Experiments I

Cited by 251 publications

References 16 publications

Anharmonicity and atomic distribution of SnTe and PbTe thermoelectrics

Anharmonicity and atomic distribution of SnTe and PbTe thermoelectrics

Phonon softening and metallization of a narrow-gap semiconductor by thermal disorder

Dispersion of the high-energy phonon modes inNd1.85Ce0.15CuO4

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